Re: Inverted V dipoles

---------

From: robert bowman (bowman@montana.com)
Date: Tue May 14 1996 - 22:32:14 EDT


>I am thinking about building an inverted V
> If I am not mistaken if the lines are 90 degrees apart then the antenna has
 an impedance of 300 ohms.

1994 ARRL Handbook, pg 17-6: the input impedances of antennas (inverted V)
with apex heights of .2 lambda and apex angles of 127 degrees and 90 degrees are
50 and 36 ohms, respectively. the ohm values stated for an antenna assume
that it is resonant at the frequency of interest, so its really 50 + j0, for
instance.
if the antenna is long or short, it will look inductive or capacitive.

>BTW how does one generally measure the impedance of an antenna.

a noise bridge is handy. you can either measure at the feedpoint, or at the
end of a transmission line, and use the equations to derive the feedpoint
complex impedance.

a grid dip helps, too. you can trim the antenna to resonance, or add coils or
capacitance as needed. that 'divide 234 by the frequency' rule of thumb needs
to be taken with a big box of Morton's finest. everything in the near
vicinity gets
into play, including the trees, gutters, etc. if you know the system is
resonant,
and you have a ballpark number for the expected radiation resistance, and the
loss resistances, the swr should confirm things.

inverted vees make a nice multiband with a little forethought. i used pvc
rings to
break the legs into appropriate segments, and jumpered them together for the
lower bands.


Search QRP-L Archives

[ QRP-L Archive | ]
[ 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 ]

---------

This archive was generated by hypermail 2b29 on Fri Jun 02 2000 - 11:30:18 EDT

kd4ab@kd4ab.org